The copending patent application Ser. No. 10/452,738 (“the '738 application”) addresses the problem where federal, state and local agencies require many types of batteries, including primary or rechargeable batteries, for example lithium batteries as one example only, to be discharged completely prior to discarding the battery. Many batteries must be disposed of in a reliable manner because of the inherent risk of fire or explosion created by the improper use or disposal of batteries. As hazardous batteries become more commonplace to power personal and commercial equipment, it is necessary to improve battery discharge systems associated with these types of hazardous batteries and overcome prior art reliability problems in battery discharge, such as caused by moving components, and/or sealing problems. Often, water seeps into a battery casing. If a cell is hazardous, such as lithium, and contacts the water, it could explode. Thus, it is required to fully dissipate any battery charge, such as a lithium battery, before it can be disposed to minimize the chance of explosion or fire.
Typically, prior art batteries have often been discharged using external clip leads and resistors. This method is generally crude and unreliable. It could also create a shock potential. Other battery discharge systems offer some improvement, but still pose problems. For example, U.S. Pat. No. 6,270,916 to Sink et al. discloses a complete discharge device for a lithium battery that is more reliable than an external clip and resistor. It uses internal electromechanical switches and resistors, and “pull tabs” that are accessed via access holes formed in the battery case. This type of battery Complete Discharge Device (CDD) uses a CDD actuator that is or may be prone to self-activation under physical abuse conditions. A switch, formed of a switch contact, such as a spring contact, is biased toward a contact pad. When the contact and contact pad meet, the discharge circuit is activated. Other prior art battery discharge devices use switches that can be actuated by knobs, handles or screws. These actuation devices can typically be accessed from outside the battery by removing a watertight cover or instruction label.
Other patents disclose different types of battery discharge systems, such as U.S. Pat. Nos. 4,407,909; 4,695,435; 5,119,009; and 5,185,564. The '009 patent discloses another manually operated switch that selectively couples the discharge mechanism to at least one lithium cell to complete discharge. The '564 patent discloses a battery discharge apparatus using a strap for mounting a housing to a battery and having adjustable contact members. Similar to other prior art battery discharge mechanisms and systems, these disclosed systems could be unreliable because they often use electromechanical and/or other types of moving or unreliable parts.
There is also a requirement that batteries be watertight. This requirement becomes critical when the battery contains a lithium cell that could explode upon contact with water. To meet this stringent design requirement, a watertight seal is often provided between the battery casing and any actuator used for actuating a battery discharge circuit. In some battery designs, this is accomplished by using a “peel off” label over an access hole, or a nylon seal positioned between an actuator and a battery casing. These seals, however, have often proven unreliable, particularly when the internal pressure in the battery increases because of temperature changes or altitude changes.
The invention set forth in the '738 application overcomes these reliability and sealing problems for these batteries. In the '738 application, a light sensing circuit is used and contains no moving parts, and is connected to a battery discharge circuit such that the battery discharge circuit is actuated after exposing to light the light sensing circuit.
The light sensing circuit is preferably mounted within the battery. The battery can have an opening (preferably watertight) formed in the battery casing through which ambient light enters for exposing the light sensing circuit. A removable, opaque cover is positioned over the opening and blocks light from passing onto the light sensing circuit. Upon removal of the opaque cover, the light sensing circuit is exposed to light. A lense is preferably positioned and sealed in a watertight manner at the opening to prevent water from passing into the battery and engaging a battery, for example, a lithium cell or other similarly hazardous cell. The lense allows light through the opening and onto the light sensing circuit upon removal of the cover. In one aspect of the present invention, the cover comprises a removable label adhesively secured onto the battery. A latching circuit can latch the battery discharge circuit into an “ON” condition to maintain battery discharge even when the light sensing circuit is no longer exposed to light.
There are also different functions associated with battery discharge circuits. One of these functions is a heating circuit. Examples of battery heating circuits include those disclosed in U.S. Pat. Nos. 3,440,109; 3,623,916; 5,508,126; 5,599,636; 5,795,664; 5,834,131; 5,990,661; 6,002,240; 6,072,301; 6,078,163; 6,259,229; 6,392,388; and 6,441,588.
One drawback that may not be adequately addressed by prior art proposals is that associated with the increase in internal battery resistance, which increases significantly at these lower temperatures. In most battery applications, the equipment being powered by the cell or battery has a minimum operating voltage, commonly called the “cut-off voltage.” A reduced terminal voltage at lower temperatures causes the powered equipment to reach its cut-off voltage prematurely, while the cell or battery has much remaining stored capacity. This phenomenon becomes dominant at the lower 10° C. or so of the cell or battery specified operating temperature range. In some cases at the minimum, specified operating temperature, it is possible to obtain only 10% or 20% of the total capacity from the cell or battery. It would be advantageous to develop a battery and circuit that would overcome this problem in a reliable and acceptable, but cost effective and simple manner.
There is also a problem with some prior art batteries of intentional or inadvertent attempts to charge primary cells or batteries, but instead causing catastrophic failures of the cell or battery. As a result, many battery customers specify that some type of charge protection be provided within a battery. Many current charge protection technologies use diodes in series with each string of cells or batteries to prevent charging. While the use of diodes performs an intended function, it has some drawbacks. For example, in many battery applications, the equipment being powered by the cell or battery has a minimum operating voltage, commonly called the “cut-off voltage.” Some charge protection diodes typically have a forward drop or loss of about 300 millivolts to 1 volt or more. The diode loss causes the powered equipment to reach its cut-off voltage prematurely, while the cell or battery has much remaining stored capacity. Also, the diode dissipates power that is delivered by the cell or battery, but is not delivered to the load. This phenomenon is aggravated at lower operating temperatures because the internal resistance of the cell or battery increases at lower temperatures and thereby lowers its terminal voltage. It would be advantageous if a battery and circuit could be developed to minimize diode loss and provide charge protection and diode replacement.
In other battery applications, there are two voltage limits that the battery must meet. There is an open circuit voltage that must not be exceeded. If it is exceeded, damage to the load that the battery is powering could occur. There is also a minimum operating or cut-off voltage that must be maintained or the load that the battery is powering may cease to function. Because of internal resistance of the cells in a battery, the cell voltage drops significantly as a load is applied. This problem is aggravated at colder temperatures.
Generally, the voltage requirements can be met by stacking as many series cells as possible without exceeding the open circuit voltage. Many parallel strings of cells are then added as required to meet the cut-off voltage under the battery load and temperature operating requirements. This approach is effective, but normally requires adding more cells than would normally be required. Besides adding weight and cost to the overall application, this approach may not fit some physical space limitations. An alternative approach has been the use of voltage regulation circuitry such as DC-to-DC converters. This approach may also be an improvement over adding parallel strings or cells, but it is costly, complex and tends to be energy inefficient.
It would be advantageous if a battery and circuit could be used for overcoming the above-noted problems.